1 April 2015

Hemcrete homes deliver low-energy living

The final report on the Renewable House Project, delivered by NNFCC on behalf of DECC, shows that building homes with Hemcrete can provide substantial carbon savings - but further work is needed to ensure consistent build quality

In 2009, NNFCC delivered the Renewable House Project on behalf of the Department for Energy and Climate Change (DECC), demonstrating the potential for use of Hemcrete construction methods in the development of affordable sustainable housing.

What is Hemcrete?

Hemcrete is a building material that uses hemp in its mixture. The inside stem of the hemp plant is mixed with a lime-based binder to create a versatile building material that can be used for wall insulation, flooring, walls, roofing and more. Unlike concrete, Hemcrete can have a negative carbon footprint, so has huge potential for helping the construction industry to reduce emissions and become sustainable.

The house constructed for the project achieved a Code Level 4 sustainability rating assessment against the Code for Sustainable Homes, at a build cost of £75,000.

Developing the renewable construction industry

In 2009-10, the Government invested £6.3m under the Low Carbon Investment Fund (LCIF) to support the construction of 283 low carbon affordable homes; built with a range of innovative renewable materials.  The aim was to spur interest in and the development of the renewable construction materials industry, and to engage the affordable housing sector in the low carbon agenda.

With support from DECC and funding from the Low Carbon Innovation Fund (LCIF), a further project was commissioned to examine the energy performance of a selection of the renewable housing within the new developments.

Key points from the findings included:

  • Construction methods of Hemcrete houses can be up to 30% less than traditional brick-block methods
  • Hemcrete houses can cost less to heat and occupants can reduce their energy consumption costs.

However, ensuring lower energy consumption by occupants was dependent on rigorous control of construction, and appropriate use of novel renewable heating using air-source heat pumps and mechanical ventilation systems.

The report shows that cases of the houses not performing as hoped were caused by build quality issues, including issues around air tightness.

Additional simulation work found that addressing build-quality issues could result in energy consumption in Hemcrete houses being 50-80% lower than in conventionally-constructed houses.

Industry has responded to issues caused by poor weather affecting the drying of Hemcrete in winter, by developing factory-made panel systems.

Variability in the performance of Air Source Heat Pumps was also highlighted, particularly when linked to hot water systems, with family occupants using the heat boost function or additional immersion heaters, increasing energy demand.

There are a number of important lessons for future similar developments:

  • Construction site workers need to be better trained to work with Hemcrete, to ensure design parameters are more likely to be achieved;
  • Education and communication on energy issues improves performance. This was particularly evident in situations where contractors received specialist training, particularly in use of heat pumps;
  • Maintenance service providers need training in renewable energy technologies, such as air source heat pumps, in order to deal with performance issues.

The report concludes that Hemcrete has considerable potential for transforming the UK construction industry. When used correctly, Hemcrete can facilitate substantial carbon emissions savings for the UK. Further work is needed to develop this material, and a closer collaboration is needed between designers, developers, users and researchers.

To read the full report click here.

Source: NNFCC, press release, 2015-03-26.


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